Assist control device

ABSTRACT

An assist control device controls an electric motor assisting traveling of a mobile object. The assist control device includes an operating switch and a control part. The operating switch is configured to be turned on when operated by a user. The operating switch is configured to be turned off when released from being operated by the user. The control part controls the electric motor to output an assist force when the operating switch is turned on.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No.2021-140120 filed Aug. 30, 2021. The entire contents of that applicationare incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to an assist control device.

BACKGROUND ART

It has been proposed to enhance the performance of a mobile object movedat a low speed such as a pallet truck, a hand lift truck, a hand truck,or a wheelchair by attaching a drive unit thereto. The drive unitincludes an electric motor for rotationally driving a wheel, a controldevice for controlling the electric motor, and so forth. When travelingof the mobile object is made by a human drive force, the electric motoroutputs an assist force for assisting the human drive force.

For example, Publication of Japan Patent No. 4495444 discloses a type ofcontrol device configured to cause the electric motor to output theassist force depending on the acceleration of the mobile object.

The control device configured as described above has the followingconcern: when a user leans against the mobile object or when the mobileobject is disposed on the surface of a slope, the mobile object startsmoving, and accordingly, the electric motor outputs an assist forcedepending on the acceleration of the mobile object, even though theassist force is not intended by the user.

It is an object of the present invention to prevent outputting anunintended assist force.

BRIEF SUMMARY

An assist control device according to an aspect of the present inventioncontrols an electric motor assisting traveling of a mobile object. Theassist control device includes an operating switch and a control part.The operating switch is configured to be turned on when operated by auser. The operating switch is also configured to be turned off whenreleased from being operated by the user.

The control part controls the electric motor to output an assist forcewhen the operating switch is turned on.

According to this configuration, the electric motor does not output theassist force unless the operating switch is turned on when operated bythe user. Hence, the electric motor can be prevented from outputting theassist force unintended by the user.

Preferably, the operating switch includes a forward movement switch anda reverse movement switch. The control part controls the electric motorto output the assist force for forward movement when the forwardmovement switch is turned on. By contrast, the control part controls theelectric motor to output the assist force for reverse movement when thereverse movement switch is turned on.

Preferably, the operating switch is configured to be turned on as eithera first on state or a second on state when operated by the user. Theoperating switch is configured to be turned off when released from beingoperated by the user. The control part controls the electric motor tooutput the assist force for forward movement when the operating switchis turned on as the first on state. By contrast, the control partcontrols the electric motor to output the assist force for reversemovement when the operating switch is turned on as the second on state.

Preferably, the mobile object further includes an operating handle thatextends upward and is configured to be pivotable. The assist controldevice further includes a tilt angle detection part detecting a tiltangle of the operating handle relative to a vertical axis. The controlpart controls the electric motor based on the tilt angle detected by thetilt angle detection part.

Preferably, the control part determines whether the tilt angle is in afirst range, a second range, or a third range. The second range isgreater in the tilt angle than the first range. The third range isgreater in the tilt angle than the second range. Besides, the controlpart stops the electric motor from assisting when determining that thetilt angle is in the third range.

Preferably, the tilt angle detection part is formed by at least one ofan acceleration sensor, a gyro sensor, and a limit switch.

Preferably, the control part executes first brake processing forstopping the mobile object when determining that the operating switch isswitched off from on during traveling of the mobile object.

Preferably, the control part executes the first brake processing afterelapse of a predetermined waiting time.

Preferably, the control part executes second brake processing forstopping the mobile object when determining that both the forwardmovement switch and the reverse movement switch are turned on duringtraveling of the mobile object.

Preferably, the control part executes third brake processing forstopping the mobile object when determining either that the reversemovement switch is turned on during forward movement of the mobileobject or that the forward movement switch is turned on during reversemovement of the mobile object.

Preferably, the control part executes the third brake processing forstopping the mobile object when determining that the operating switch isswitched between the first on state and the second on state duringtraveling of the mobile object.

Preferably, the control part executes the brake processing with a brakeforce depending on the assist force of the electric motor.

Preferably, the control part calculates the assist force based on mobileobject information regarding the mobile object. It should be noted thatthe acceleration, velocity, weight, and so forth of the mobile object,for instance, can be exemplified as the mobile object information.

Preferably, the control part stops calculation of the assist force andsets the assist force to a preliminarily set value until the mobileobject reaches a preliminarily set vehicle velocity from starting ofassist control.

Preferably, the control part stops calculation of the assist force andsets the assist force to the preliminarily set value until apreliminarily set time elapses from starting of assist control.

Preferably, the control part sets the assist force to zero when themobile object stands still after elapse of the preliminarily set time.

Overall, according to the present invention, it is possible to preventoutputting an unintended assist force.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of part of a pallet truck.

FIG. 2 is a block diagram of a drive unit.

FIG. 3 is a flowchart showing a plurality of processing executed by acontrol part.

FIG. 4 is a flowchart showing one processing executed by the controlpart.

FIG. 5 is a flowchart showing the one processing executed by the controlpart.

FIG. 6 is a flowchart showing another processing executed by the controlpart.

FIG. 7 is a flowchart showing the another processing executed by thecontrol part.

FIG. 8 is a flowchart showing yet another processing executed by thecontrol part.

FIG. 9 is a flowchart showing the yet another processing executed by thecontrol part.

FIG. 10 is a timing chart for explaining traveling of the pallet truck.

DETAILED DESCRIPTION

An assist control device according to an embodiment of the presentinvention will be hereinafter explained with reference to drawings. Theassist control device (hereinafter simply referred to as “controldevice” on an as-needed basis) is configured to control an electricmotor for assisting traveling of a mobile object. The control device isinstalled in the mobile object. It should be noted that traveling of themobile object is made by a human drive force. The mobile object is movedat a low speed. The mobile object is configured to transport an object.It should be noted that the term “object” is conceptualized asencompassing a person or so forth as well. A pallet truck, a hand lifttruck, a hand truck, a wheelchair, or so forth is exemplified as themobile object described above. It should be noted that in the presentembodiment, the mobile object is the pallet truck.

<Pallet Truck>

FIG. 1 is a side view of a pallet truck 200 in which the control deviceis installed. As shown in FIG. 1 , the pallet truck 200 includes apallet truck body 210 and a drive unit 20. The pallet truck body 210includes a loading platform (a pair of fork arms) 201, an operatinghandle 202, and a plurality of vehicle wheels 204. The drive unit 20 isattached to the pallet truck body 210.

When the pallet truck 200 is moved leftward in FIG. 1 , the movement isdefined as forward movement; conversely, when the pallet truck 200 ismoved rightward in FIG. 1 , the movement is defined as reverse movement.Specifically, when the user pulls the operating handle 202, the pallettruck 200 is forwardly moved; conversely, when the user pushes theoperating handle 202, the pallet truck 200 is reversely moved.

The operating handle 202 upwardly extends from the loading platform 201.Besides, the operating handle 202 is configured to be pivotable about abase end 202 a. It should be noted that when pivoted, the operatinghandle 202 is tilted relative to a vertical axis V. A tilt angle θ,formed by the operating handle 202 and the vertical axis V, ischangeable by pivoting the operating handle 202 about the base end 202a.

The range of the tilt angle θ formed by the operating handle 202 and thevertical axis V can be divided into a first range R1, a second range R2,and a third range R3. It should be noted that when the operating handle202 is tilted within the first range R1, the tilt angle θ becomes thesmallest; when the operating handle 202 is tilted within the secondrange R2, the tilt angle θ is larger than that when the operating handle202 is tilted within the first range R1; when the operating handle 202is tilted within the third range R3, the tilt angle θ is larger thanthat when the operating handle 202 is tilted within the second range R2.

For example, the range of the tilt angle θ can be set as follows, albeitnot particularly limited thereto: the first range R1 is 0°≤θ≤20°; thesecond range R2 is 20°≤θ≤60′; the third range R3 is 60°≤θ≤90°. Thus,when tilted within the first range R1, the operating handle 202 can beregarded as set in an upright state. On the other hand, when tiltedwithin the second range R2, the operating handle 202 can be regarded asset in a tilt state. Yet on the other hand, when tilted within the thirdrange R3, the operating handle 202 can be regarded as set in a lyingstate.

<Drive Unit>

As shown in FIG. 2 , the drive unit 20 includes an electric motor 21, amotor driver 22, a reducer 23, a battery 24 (see FIG. 1 ), a drive wheel203, and a control device 100. It should be noted that the drive unit 20may not include the drive wheel 203. In this case, the drive unit 20rotationally drives at least one of the vehicle wheels 204 of the pallettruck 200 instead of the drive wheel 203.

The electric motor 21 outputs an assist force for assisting traveling ofthe pallet truck 200. The electric motor 21 rotationally drives thedrive wheel 203.

The motor driver 22 controls electricity to be supplied to the electricmotor 21 from the battery 24. The motor driver 22 is connected to thecontrol device 100 by wired or wireless means in communicable manner.The motor driver 22 drives the electric motor 21 in accordance with acontrol signal inputted thereto from the control device 100.

The reducer 23 reduces the speed of rotation of the electric motor 21and transmits the rotation reduced in speed to the drive wheel 203. Thereducer 23 is composed of, for instance, a plurality of gears and soforth.

<Control Device>

The control device 100 is configured to control the electric motor 21.The control device 100 includes an operating switch 3, a tilt angledetection part 4, and a control part 10.

The operating switch 3 is attached to, for instance, the operatinghandle 202. When operated by the user, the operating switch 3 isconfigured to be turned on; conversely, when released from beingoperated by the user, the operating switch 3 is configured to be turnedoff. In other words, the operating switch 3 is of a momentary type.

The operating switch 3 includes, for instance, a forward movement switch3 a and a reverse movement switch 3 b. Both the forward movement switch3 a and the reverse movement switch 3 b are of the momentary type.

When the assist force is required in forward traveling, the useroperates the forward movement switch 3 a. For example, the forwardmovement switch 3 a is a push-button switch. The user pushes the forwardmovement switch 3 a. Only when kept pushed, the forward movement switch3 a is turned on.

Then, when released from being operated by the user, the forwardmovement switch 3 a is turned off. For example, when the forwardmovement switch 3 a, kept pushed by a finger of the user, is releasedfrom the finger, the forward movement switch 3 a is turned off. Itshould be noted that the forward movement switch 3 a is not limited tothe push-button switch, and alternatively, for instance, can be a switchwith a touch sensor such as a capacitive touch switch.

When the assist force is required in reverse traveling, the useroperates the reverse movement switch 3 b. For example, the reversemovement switch 3 b is a push-button switch. The user pushes the reversemovement switch 3 b. Only when kept pushed, the reverse movement switch3 b is turned on.

Then, when released from being operated by the user, the reversemovement switch 3 b is turned off. For example, when the reversemovement switch 3 b, kept pushed by a finger of the user, is releasedfrom the finger, the reverse movement switch 3 b is turned off. Itshould be noted that the reverse movement switch 3 b is not limited tothe push-button switch, and alternatively, for instance, can be a switchwith a touch sensor such as a capacitive touch switch.

It should be noted that when the assist force is not required, the userdoes not operate both the forward movement switch 3 a and the reversemovement switch 3 b.

The tilt angle detection part 4 is configured to detect the tilt angle θof the operating handle 202 relative to the vertical axis V. Forexample, an acceleration sensor can be provided as the tilt angledetection part 4. Alternatively, a gyro sensor can be provided as thetilt angle detection part 4. Yet alternatively, both the accelerationsensor and the gyro sensor can compose the tilt angle detection part 4.Still alternatively, a tilt sensor, an angle sensor, a limit switch, orso forth can be provided as the tilt angle sensor 4. It should be notedthat when the limit switch is employed, the tilt angle detection part 4detects not a tilt angle per se but a tilt range.

For example, a computer (e.g., microcomputer), including a CPU (CentralProcessing Unit), a ROM (Read Only Memory), and so forth, is provided asthe control part 10. The ROM stores programs for various computations.The CPU executes the programs stored in the ROM.

The control part 10 is configured to control the electric motor 21. Whenthe operating switch 3 is turned on, the control part 10 causes theelectric motor 21 to output the assist force.

Speaking in detail, when determining that the forward movement switch 3a is turned on, the control part 10 controls the electric motor 21 tooutput the assist force for forward movement. Accordingly, the electricmotor 21 outputs the assist force for forward movement to rotationallydrive the drive wheel 203. The processing described herein, executed bythe control part 10 to cause the electric motor 21 to output the assistforce for forward movement, will be referred to as “forward movementassist processing”.

On the other hand, when determining that the reverse movement switch 3 bis turned on, the control part 10 controls the electric motor 21 tooutput the assist force for reverse movement. Accordingly, the electricmotor 21 outputs the assist force for reverse movement to rotationallydrive the drive wheel 203. The processing described herein, executed bythe control part 10 to cause the electric motor 21 to output the assistforce for reverse movement, will be referred to as “reverse movementassist processing”.

It should be noted that the assist force for forward movement and thatfor reverse movement can be calculated by the control part 10 based on,for instance, mobile object information regarding the pallet truck 200.It should be noted that the acceleration of the pallet truck 200, theweight of the pallet truck 200 including an object loaded thereon,rolling resistance, power loss, and so forth can be exemplified as themobile object information.

Specifically, an assist force F_(a) can be calculated by the controlpart 10 based on the following formula (1).

[Math. 1]

F _(a) =αF  (1)

Here, “α” indicates an assist ratio. The assist ratio α is greater than0 and less than 1.

“F” in the formula (1) can be calculated by the control part 10 based onthe following formula (2).

[Math.2]

F=Ma+F _(v) +F _(r) +Mg sin θ  (2)

Here, “M” indicates the weight of the pallet truck 200 including anobject loaded thereon; “a” indicates the acceleration of the pallettruck 200; “F_(v)” indicates power loss; “F_(r)” indicates rollingresistance; “g” indicates gravitational acceleration; “0” indicates thetilt angle of the road surface on which the pallet truck 200 travels.The user is allowed to input a value of the weight M.

The power loss F_(v) can be calculated by the control part 10 based onthe following formula (3).

[Math.3]

F _(v) =kV+C  (3)

It should be noted that “kV” indicates shaft viscosity resistance; “k”indicates shaft viscosity coefficient. “C” indicates power lossexcluding the shaft viscosity resistance and is, for instance, the sumof power loss including transmission loss of a chain or so forth,bearing friction, and so forth.

On the other hand, the rolling resistance F_(r) can be calculated by thecontrol part 10 based on the following formula (4).

[Math. 4]

F _(r) =C _(rr) Mg cos θ  (4)

It should be noted that “C_(rr)” indicates rolling resistancecoefficient.

It should be noted that the control part 10 outputs a control signal tothe motor driver 22 to control the electric motor 21. The control part10 determines whether or not the pallet truck 200 is traveling based on,for instance, the velocity, the acceleration, or so forth of the pallettruck 200. Besides, the control part 10 determines in which of theforward and reverse directions the pallet truck 200 is traveling basedon the velocity, the acceleration, or so forth of the pallet truck 200.

When determining that the forward movement switch 3 a is turned off, andsimultaneously, the reverse movement switch 3 b is turned off, thecontrol part 10 does not cause the electric motor 21 to output theassist force for forward movement and that for reverse movement. In thiscase, traveling of the pallet truck 200 is made only by a human driveforce. Traveling of the pallet truck, made only by the human drive forceas described above, will be hereinafter referred to as “free traveling”.

The control part 10 controls the electric motor 21 based on the tiltangle θ of the operating handle 202. First, the control part 10determines whether the tilt angle θ of the operating handle 202 relativeto the vertical axis V is in the first range R1, the second range R2, orthe third range R3.

When determining that the tilt angle θ is in the first range R1, thecontrol part 10 does not cause the electric motor 21 to output theassist force even if the forward movement switch 3 a is turned on. Inother words, when the tilt angle θ is in the first range R1, the controlpart 10 does not execute the forward movement assist processing. In thiscase, the user enables the pallet truck 200 to perform free traveling.It should be noted that when the reverse movement switch 3 b is turnedon, the control part 10 causes, as usual, the electric motor 21 tooutput the assist force for reverse movement. In other words, thecontrol part 10 executes the reverse movement assist processing.

On the other hand, when determining that the tilt angle θ is in thesecond range R2, the control part 10 causes, as usual, the electricmotor 21 to output the assist force for both forward movement andreverse movement. In other words, when the tilt angle θ is in the secondrange R2, the control part 10 is enabled to execute the forward movementassist processing and the reverse movement assist processing.

Yet on the other hand, when determining that the tilt angle θ is in thethird range R3, the control part 10 does not cause the electric motor 21to output the assist force even if the forward movement switch 3 a isturned on as well as if the reverse movement switch 3 b is turned on.Thus, when the tilt angle θ is in the third range R3, the control part10 neither executes the forward movement assist processing nor thereverse movement assist processing. Because of this, free traveling isonly enabled by the pallet truck 200.

When determining that the operating switch 3 is switched off from onduring traveling of the pallet truck 200, the control part 10 executesfirst brake processing for stopping the pallet truck 200. For example,the control part 10 executes the first brake processing when the forwardmovement switch 3 a is switched off from on during forward movement ofthe pallet truck 200, or alternatively, when the reverse movement switch3 b is switched off from on during reverse movement of the pallet truck200. When determining that the pallet truck 200 has been stopped, thecontrol part 10 stops executing the first brake processing.

For example, regenerative braking of the electric motor 21, shortbraking of the electric motor 21, and so forth can be exemplified as thefirst brake processing. The control part 10 outputs a control signal tothe motor driver 22 such that regenerative braking or short braking ofthe electric motor 21 can be executed. It should be noted that a brakedevice can be installed in the pallet truck 200; then, the control part10 can control the brake device to stop the pallet truck 200.

The control part 10 executes the first brake processing after elapse ofa predetermined waiting time. In other words, when determining that theforward movement switch 3 a is switched off from on or that the reversemovement switch 3 b is switched off from on, the control part 10executes the first brake processing after elapse of the predeterminedwaiting time without executing the first brake processing immediately.

It should be noted that the predetermined waiting time can be set toabout 0.3 to 1.0 second, for instance, albeit not particularly limitedthereto. Besides, the predetermined waiting time can be set to a fixedtime preliminarily stored in the control part 10. It should be notedthat alternatively, the waiting time can be set by the control part 10depending on the velocity or weight of the pallet truck 200. Forexample, the waiting time can be reduced by the control part 10 withincrease in velocity of the pallet truck 200. Alternatively, the waitingtime can be reduced by the control part 10 with increase in weight ofthe pallet truck 200 (including the object loaded thereon).

When determining that both the forward movement switch 3 a and thereverse movement switch 3 b are turned on during traveling the pallettruck 200, the control part 10 executes a second brake processing forstopping the pallet truck 200. When determining that the pallet truck200 has been stopped, the control part 10 stops executing the secondbrake processing.

For example, when the user operates (pushes) both the forward movementswitch 3 a and the reverse movement switch 3 b during free traveling ofthe pallet truck 200, the control part 10 executes the second brakeprocessing.

On the other hand, under the condition that the user operates theforward movement switch 3 a to cause the pallet truck 200 to performforward movement-assisted traveling, the control part 10 executes thesecond brake processing when the user further operates the reversemovement switch 3 b, while keeping operating the forward movement switch3 a.

Yet on the other hand, under the condition that the user operates thereverse movement switch 3 b to cause the pallet truck 200 to performreverse movement-assisted traveling, the control part 10 executes thesecond brake processing when the user further operates the forwardmovement switch 3 a, while keeping operating the reverse movement switch3 b.

It should be noted that for example, regenerative braking of theelectric motor 21, short braking of the electric motor 21, and so forthcan be exemplified as the second brake processing. The control part 10outputs a control signal to the motor driver 22 such that regenerativebraking or short braking of the electric motor 21 can be executed. Itshould be noted that the brake device described above or another brakedevice can be installed in the pallet truck 200; then, the control part10 can control the brake device to stop the pallet truck 200. A brakeforce generated in the second brake processing can be equal in magnitudeto or different in magnitude from that generated in the first brakeprocessing.

The control part 10 can execute a third brake processing for stoppingthe pallet truck 200 when determining that the reverse movement switch 3b is turned on during forward movement of the pallet truck 200 or thatthe forward movement switch 3 a is turned on during reverse movement ofthe pallet truck 200. It should be noted that regenerative braking ofthe electric motor 21, short braking of the electric motor 21, brakingof the brake device, and so forth can be exemplified as the third brakeprocessing similarly to those exemplified as the second brakeprocessing. When determining that the pallet truck 200 has been stopped,the control part 10 stops executing the third brake processing.

The control part 10 executes each of the first to third brake processingwith a brake force depending in magnitude on the assist force of theelectric motor 21. For example, the control part 10 increases the brakeforce in each of the first to third brake processing with increase inmagnitude of the assist force of the electric motor 21. It should benoted that the control part 10 can execute each of the first to thirdbrake processing with a fixed brake force regardless of the magnitude ofthe assist force of the electric motor 21. [Control Method]

Next, an example of a plurality of processing executed by the controlpart 10 will be explained with reference to a flowchart shown in FIG. 3.

First, based on the tilt angle θ detected by the tilt angle detectionpart 4, the control part 10 determines whether the tilt angle θ of theoperating handle 202 is in the first range R1, the second range R2, orthe third range R3. Specifically, the control part 10 determines whetheror not the tilt angle θ is in the first range R1 (step S1).

When determining that the tilt angle θ is in the first range R1 (Yes instep S1), the control part 10 executes first processing to be described(step S2).

Next, the control part 10 determines whether or not the tilt angle θ isin the second range R2 (step S3). When determining that the tilt angle θis in the second range R2 (Yes in step S3), the control part 10 executessecond processing to be described (step S5). Conversely, whendetermining that the tilt angle θ is not in the second range R2 (No instep S3), the control part 10 executes third processing to be described(step S8).

The first processing will be explained with reference to flowchartsshown in FIGS. 4 and 5 .

First, the control part 10 determines whether or not the followingcondition is satisfied: the forward movement switch 3 a is turned off,and simultaneously, the reverse movement switch 3 b is turned off (stepS21). When determining that the following condition is satisfied: theforward movement switch 3 a is turned off, and simultaneously, thereverse movement switch 3 b is turned off (Yes in step S21), the controlpart 10 next determines whether or not the pallet truck 200 is traveling(step S22).

When determining that the pallet truck 200 is not traveling (No in stepS22), the control part 10 causes the electric motor 21 not to output theassist force. In other words, the control part 10 enables the pallettruck 200 to perform free traveling (step S23). Then, the control part10 executes processing for disabling a brake flag (step S24). It shouldbe noted that as described below, the brake flag is enabled when theoperating switch 3 is operated during traveling.

Conversely, when determining that the pallet truck 200 is traveling (Yesin step S22), the control part 10 determines whether or not the brakeflag is enabled (step S25).

When determining that the brake flag is enabled (Yes in step S25), thecontrol part 10 executes the first brake processing (step S26).Conversely, when determining that the brake flag is not enabled (No instep S25), the control part 10 causes the electric motor 21 not tooutput the assist force. In other words, the control part 10 enables thepallet truck 200 to perform free traveling (step S27).

When determining in step S21 described above that the followingcondition is not satisfied: the forward movement switch 3 a is turnedoff, and simultaneously, the reverse movement switch 3 b is turned off(No in step S21), the control part 10 next determines whether or not thefollowing condition is satisfied: the forward movement switch 3 a isturned on, and simultaneously, the reverse movement switch 3 b is turnedoff (step S28).

When determining that the following condition is satisfied: the forwardmovement switch 3 a is turned on, and simultaneously, the reversemovement switch 3 b is turned off (Yes in step S28), the control part 10next determines whether or not the pallet truck 200 is traveling (stepS29).

When determining that the pallet truck 200 is not traveling (No in stepS29), the control part 10 causes the electric motor 21 not to output theassist force. In other words, the control part 10 enables the pallettruck 200 to perform free traveling (step S30). Then, the control part10 executes processing for disabling the brake flag (step S31).

Conversely, when determining that the pallet truck 200 is traveling (Yesin step S29), the control part 10 next determines whether or not theelectric motor 21 is forwardly rotated (step S32). It should be notedthat when the electric motor 21 is forwardly rotated, the pallet truck200 is forwardly moved. Because of this, in step S32, the control part10 can determine whether or not the pallet truck 200 is forwardly movedinstead of determining whether or not the electric motor 21 is forwardlyrotated.

When determining that the electric motor 21 is forwardly rotated (Yes instep S32), the control part 10 causes the electric motor 21 not tooutput the assist force. In other words, the control part 10 enables thepallet truck 200 to perform free traveling (step S33). Then, the controlpart 10 executes processing for enabling the brake flag (step S34).

When determining that the electric motor 21 is not forwardly rotated (Noin step S32), in other words, when determining that the electric motor21 is reversely rotated, the control part 10 causes the electric motor21 not to output the assist force. In other words, the control part 10enables the pallet truck 200 to perform free traveling (step S35). Itshould be noted that in step S35, the control part 10 can execute thethird brake processing for stopping traveling of the pallet truck 200instead of enabling the pallet truck 200 to perform free traveling.

When determining in step S28 described above that the followingcondition is not satisfied: the forward movement switch 3 a is turnedon, and simultaneously, the reverse movement switch 3 b is turned off(No in step S28), the control part 10 determines whether or not thefollowing condition is satisfied: the forward movement switch 3 a isturned off, and simultaneously, the reverse movement switch 3 b isturned on (step S36) as shown in FIG. 5 .

When determining that the following condition is satisfied: the forwardmovement switch 3 a is turned off, and simultaneously, the reversemovement switch 3 b is turned on (Yes in step S36), the control part 10next determines whether or not the pallet truck 200 is traveling (stepS37).

When determining that the pallet truck 200 is not traveling (No in stepS37), the control part 10 executes the reverse movement assistprocessing (step S38). In other words, the control part 10 causes theelectric motor 21 to output the assist force for reverse movement. Then,the control part 10 executes processing for enabling the brake flag(step S39).

Conversely, when determining that the pallet truck 200 is traveling (Yesin step S37), the control part 10 next determines whether or not theelectric motor 21 is reversely rotated (step S40). It should be notedthat when the electric motor 21 is reversely rotated, the pallet truck200 is reversely moved. Because of this, in step S40, the control part10 can determine whether or not the pallet truck 200 is reversely movedinstead of determining whether or not the electric motor 21 is reverselyrotated.

When determining that the electric motor 21 is reversely rotated (Yes instep S40), the control part 10 executes the reverse movement assistprocessing (step S41). In other words, the control part 10 causes theelectric motor 21 to output the assist force for reverse movement.Accordingly, the pallet truck 200 performs reverse movement-assistedtraveling. Then, the control part 10 executes processing for enablingthe brake flag (step S42).

When determining that the electric motor 21 is not reversely rotated (Noin step S40), in other words, when determining that the electric motor21 is forwardly rotated, the control part 10 causes the electric motor21 not to output the assist force. In other words, the control part 10enables the pallet truck 200 to perform free traveling (step S43). Itshould be noted that in step S43, the control part 10 can execute thethird brake processing for stopping traveling of the pallet truck 200instead of enabling the pallet truck 200 to perform free traveling.

When determining in step S36 described above that the followingcondition is not satisfied: the forward movement switch 3 a is turnedoff, and simultaneously, the reverse movement switch 3 b is turned on(No in step S36), the control part 10 next determines whether or not thefollowing condition is satisfied: the forward movement switch 3 a isturned on, and simultaneously, the reverse movement switch 3 b is turnedon (step S44).

When determining that the following condition is satisfied: the forwardmovement switch 3 a is turned on, and simultaneously, the reversemovement switch 3 b is turned on (Yes in step S44), the control part 10next determines whether or not the pallet truck 200 is traveling (stepS45).

When determining that the pallet truck 200 is traveling (Yes in stepS45), the control part 10 executes the second brake processing (stepS46). Conversely, when determining that the pallet truck 200 is nottraveling (No in step S45), the control part 10 causes the electricmotor 21 not to output the assist force. In other words, the controlpart 10 enables the pallet truck 200 to perform free traveling (stepS47).

The second processing will be explained with reference to flowchartsshown in FIGS. 6 and 7 .

It should be noted that processing steps S51 to S57 in the secondprocessing are identical to the processing steps S21 to S27 in the firstprocessing described above; hence, the explanation thereof will beomitted. Besides, processing steps S66 to S77 in the second processingare identical to the processing steps S36 to S47 in the first processingdescribed above; hence, the explanation thereof will be omitted.

The control part 10 determines whether or not the following condition issatisfied: the forward movement switch 3 a is turned on, andsimultaneously, the reverse movement switch 3 b is turned off (stepS58).

When determining that the following condition is satisfied: the forwardmovement switch 3 a is turned on, and simultaneously, the reversemovement switch 3 b is turned off (Yes in step S58, the control part 10next determines whether or not the pallet truck 200 is traveling (stepS59).

When determining that the pallet truck 200 is not traveling (No in stepS59), the control part 10 executes the forward movement assistprocessing (step S60). In other words, the control part 10 causes theelectric motor 21 to output the assist force for forward movement. Then,the control part 10 executes processing for enabling the brake flag(step S61).

Conversely, when determining that the pallet truck 200 is traveling (Yesin step S59), the control part 10 next determines whether or not theelectric motor 21 is forwardly rotated (step S62). It should be notedthat in step S62, the control part 10 can determine whether or not thepallet truck 200 is forwardly moved instead of determining whether ornot the electric motor 21 is forwardly rotated.

When determining that the electric motor 21 is forwardly rotated (Yes instep S62), the control part 10 executes the forward movement assistprocessing (step S63). In other words, the control part 10 causes theelectric motor 21 to output the assist force for forward movement. Then,the control part 10 executes processing for enabling the brake flag(step S64).

When determining that the electric motor 21 is not forwardly rotated (Noin step S62), in other words, when determining that the electric motor21 is reversely rotated, the control part 10 causes the electric motor21 not to output the assist force. In other words, the control part 10enables the pallet truck 200 to perform free traveling (step S65). Itshould be noted that in step S65, the control part 10 can execute thethird brake processing for stopping traveling of the pallet truck 200instead of enabling the pallet truck 200 to perform free traveling.

The third processing will be explained with reference to flowchartsshown in FIGS. 8 and 9 .

It should be noted that processing steps S81 to S95 in the thirdprocessing are identical to the processing steps S21 to S35 in the firstprocessing described above; hence, the explanation thereof will beomitted. Besides, processing steps S104 to S107 in the third processingare identical to the processing steps S44 to S47 in the first processingdescribed above; hence, the explanation thereof will be omitted.

As shown in FIG. 9 , the control part 10 determines whether or not thefollowing condition is satisfied: the forward movement switch 3 a isturned off, and simultaneously, the reverse movement switch 3 b isturned on (step S96).

When determining that the following condition is satisfied: the forwardmovement switch 3 a is turned off, and simultaneously, the reversemovement switch 3 b is turned on (Yes in step S96), the control part 10next determines whether or not the pallet truck 200 is traveling (stepS97).

When determining that the pallet truck 200 is not traveling (No in stepS97), the control part 10 causes the electric motor 21 not to output theassist force. In other words, the control part 10 enables the pallettruck 200 to perform free traveling (step S98). Then, the control part10 executes processing for disabling the brake flag (step S99).

Conversely, when determining that the pallet truck 200 is traveling (Yesin step S97), the control part 10 next determines whether or not theelectric motor 21 is reversely rotated (step S100). It should be notedthat in step S100, the control part 10 can determine whether or not thepallet truck 200 is reversely moved instead of determining whether ornot the electric motor 21 is reversely rotated.

When determining that the electric motor 21 is reversely rotated (Yes instep S100), the control part 10 causes the electric motor 21 not tooutput the assist force. In other words, the control part 10 enables thepallet truck 200 to perform free traveling (step S101). Then, thecontrol part 10 executes processing for enabling the brake flag (stepS102).

When determining that the electric motor 21 is not reversely rotated (Noin step S100), in other words, when determining that the electric motor21 is forwardly rotated, the control part 10 causes the electric motor21 not to output the assist force. In other words, the control part 10enables the pallet truck 200 to perform free traveling (step S103). Itshould be noted that in step S103, the control part 10 can execute thethird brake processing for stopping traveling of the pallet truck 200instead of enabling the pallet truck 200 to perform free traveling.

Next, the traveling state of the pallet truck 200 will be explained withreference to a timing chart shown in FIG. 10 . First, a human driveforce does not act on the pallet truck 200 until clock time t1. Besides,the forward movement switch 3 a and the reverse movement switch 3 b areturned off; hence, the electric motor 21 does not output an assistforce. Because of this, the pallet truck 200 stands still.

From clock time t1 to clock time t2, the human drive force acts on thepallet truck 200, whereby the pallet truck 200 is forwardly moved. Itshould be noted that the forward movement switch 3 a and the reversemovement switch 3 b are turned off; hence, the electric motor 21 doesnot output the assist force. In other words, the pallet truck 200performs free traveling.

At clock time t2, the forward movement switch 3 a is turned on;accordingly, the control part 10 executes the forward movement assistprocessing, whereby the electric motor 21 outputs the assist force forforward movement. Because of this, the pallet truck 200 performs forwardmovement-assisted traveling.

At clock time t3, the forward movement switch 3 a is switched off fromon; hence, at clock time t4 after elapse of a predetermined waitingtime, the control part 10 executes the first brake processing. Becauseof this, the pallet truck 200 decelerates and finally stops moving.

The pallet truck 200 thus stops moving; hence, at clock time t5, thecontrol part 10 stops executing the first brake processing. It should benoted that at this time, the electric motor 21 does not output theassist force.

At clock time t6, the reverse movement switch 3 b is turned on;accordingly, the control part 10 executes the reverse movement assistprocessing.

At clock time t7, the reverse movement switch 3 b is switched off fromon; hence, at clock time t8 after elapse of a predetermined waitingtime, the control part 10 executes the first brake processing. Then atclock time t9, both the forward movement switch 3 a and the reversemovement switch 3 b are turned on; accordingly, the control part 10executes the second brake processing. It should be noted that in thisexample, a brake force generated in the second brake processing isgreater in magnitude than that generated in the first brake processing.With the first and second brake processing, the pallet truck 200decelerates and finally stops moving.

[Modifications]

One embodiment of the present invention has been explained above.However, the present invention is not limited to the above, and avariety of changes can be made without departing from the gist of thepresent invention.

(a) In the embodiment described above, the operating switch 3 isconfigured to include two switches: the forward movement switch 3 a andthe reverse movement switch 3 b. However, the configuration of theoperating switch 3 is not limited to this. For example, a single switchcan be provided as the operating switch 3. In this case, the operatingswitch 3 is switched from one to another among three states: a first onstate, a second on state, and an off state.

The first on state of the operating switch 3 corresponds to one of thestates in the embodiment described above: the forward movement switch 3a is turned on, and simultaneously, the reverse movement switch 3 b isturned off. On the other hand, the second on state of the operatingswitch 3 corresponds to another of the states in the embodimentdescribed above: the reverse movement switch 3 b is turned on, andsimultaneously, the forward movement switch 3 a is turned off. Yet onthe other hand, the off state of the operating switch 3 corresponds toyet another of the states in the embodiment described above: the forwardmovement switch 3 a is turned off, and simultaneously, the reversemovement switch 3 b is turned off.

When operated by the user, the operating switch 3 can be set to eitherthe first on state or the second on state. Conversely, when releasedfrom being operated by the user, the operating switch 3 is configured tobe returned to the off state. In other words, the operating switch 3 isof a momentary type.

Specifically, the operating switch 3 is a toggle switch. Only while theuser tilts the operating switch 3 to a first side, the operating switch3 is set to the first on state. Then, when the user takes the hand offthe operating switch 3, the operating switch 3 is set to the off state.On the other hand, only while the user tilts the operating switch 3 to asecond side opposite to the first side, the operating switch 3 is set tothe second on state. Then, when the user takes the hand off theoperating switch 3, the operating switch 3 is set to the off state.

When determining that the operating switch 3 is set to the first onstate, the control part 10 executes the forward movement assistprocessing. In other words, the control part 10 controls the electricmotor 21 to output the assist force for forward movement. Thus, when theoperating switch 3 is set to the first on state, the control part 10executes processing identical to that executed when the forward movementswitch 3 a is turned on in the embodiment described above.

When determining that the operating switch 3 is set to the second onstate, the control part 10 executes the reverse movement assistprocessing. In other words, the control part 10 controls the electricmotor 21 to output the assist force for reverse movement. Thus, when theoperating switch 3 is set to the second on state, the control part 10executes processing identical to that executed when the reverse movementswitch 3 b is turned on in the embodiment described above.

The control part 10 does not execute the second brake processing in theembodiment described above but executes the first and third brakeprocessing in the embodiment described above.

Specifically, the control part 10 executes the first brake processingwhen determining that the operating switch 3 is switched from either thefirst on state or the second on state to the off state during travelingof the pallet truck 200. More specifically, the control part 10 executesthe first brake processing when determining that the operating switch 3is switched from the first on state to the off state during forwardmovement of the pallet truck 200. Likewise, the control part 10 executesthe first brake processing when determining that the operating switch 3is switched from the second on state to the off state during reversemovement of the pallet truck 200.

The control part 10 executes the third brake processing when determiningthat the operating switch 3 is switched between the first on state andthe second on state during traveling of the pallet truck 200.

Specifically, the control part 10 executes the third brake processingwhen determining that the operating switch 3 is switched from the firston state to the second on state during forward movement of the pallettruck 200. Likewise, the control part 10 executes the third brakeprocessing when determining that the operating switch 3 is switched fromthe second on state to the first on state during reverse movement of thepallet truck 200.

In this modification, the operating switch 3 is not set to a statecorresponding to still yet another of the states in the embodimentdescribed above: the forward movement switch 3 a is turned on, andsimultaneously, the reverse movement switch 3 b is turned on. Hence, thecontrol part 10 does not execute the processing steps S44 to S47, theprocessing steps S74 to S77, and the processing steps S104 to S107 inthe embodiment described above.

(b) The control part 10 can stop calculating the assist force eitheruntil the pallet truck 200 reaches a preliminarily set vehicle velocityfrom starting of assist control or until a preliminarily set timeelapses after starting of assist control. The control part 10 can setthe assist force to a preliminarily set value instead of calculating theassist force. It should be noted that the preliminarily set value maynot be a fixed value. Besides, starting of assist control can be definedas the timing when the forward movement switch 3 a or the reversemovement switch 3 b is turned on.

The control part 10 can set the assist force to zero when determiningthat the pallet truck 200 stands still even after elapse of apreliminarily set time. Alternatively, the control part 10 can controlthe assist force based on both the vehicle velocity and the elapsedtime.

REFERENCE SIGNS LIST

-   3: Operating switch-   3 a: Forward movement switch-   3 b: Reverse movement switch-   4: Tilt angle detection part-   10: Control part-   21: Electric motor-   100: Control device-   200: Pallet truck-   202: Operating handle-   R1: First range-   R2: Second range-   R3: Third range

What is claimed is:
 1. An assist control device controlling an electricmotor assisting traveling of a mobile object, the assist control devicecomprising: an operating switch configured to be turned on when operatedby a user, the operating switch configured to be turned off whenreleased from being operated by the user; and a control part configuredto control the electric motor to output an assist force when theoperating switch is turned on.
 2. The assist control device according toclaim 1, wherein the operating switch includes a forward movement switchand a reverse movement switch, and the control part is furtherconfigured to control the electric motor to output the assist force forforward movement when the forward movement switch is turned on, thecontrol part being further configured to control the electric motor tooutput the assist force for reverse movement when the reverse movementswitch is turned on.
 3. The assist control device according to claim 1,wherein the operating switch is configured to be turned on as either afirst on state or a second on state when operated by the user, theoperating switch being further configured to be turned off when releasedfrom being operated by the user, and the control part is furtherconfigured to control the electric motor to output the assist force forforward movement when the operating switch is turned on as the first onstate, the control part being further configured to control the electricmotor to output the assist force for reverse movement when the operatingswitch is turned on as the second on state.
 4. The assist control deviceaccording to claim 1, further comprising: an angle detection partconfigured to detect an angle, wherein the mobile object includes anoperating handle extending upward, the operating handle configured to bepivotable, the angle detection part is further configured to detect atilt angle of the operating handle relative to a vertical axis, and thecontrol part is further configured to control the electric motor basedon the tilt angle detected by the angle detection part.
 5. The assistcontrol device according to claim 4, wherein the control part isconfigured to determine whether the tilt angle is in a first range, asecond range, or a third range, the second range being greater in thetilt angle than the first range, the third range being greater in thetilt angle than the second range, the control part being configured tostop the electric motor from assisting when determining that the tiltangle is in the third range.
 6. The assist control device according toclaim 4, wherein the angle detection part is formed by at least one ofan acceleration sensor, a gyro sensor, or a limit switch.
 7. The assistcontrol device according to claim 1, wherein the control part isconfigured to execute first brake processing to stop the mobile objectwhen determining that the operating switch is switched off from onduring traveling of the mobile object.
 8. The assist control deviceaccording to claim 7, wherein the control part is further configured toexecute the first brake processing after elapse of a predeterminedwaiting time.
 9. The assist control device according to claim 2, whereinthe control part is further configured to execute second brakeprocessing to stop the mobile object when determining that both theforward movement switch and the reverse movement switch are turned onduring traveling of the mobile object.
 10. The assist control deviceaccording to claim 2, wherein the control part is further configured toexecute third brake processing to stop the mobile object whendetermining either that the reverse movement switch is turned on duringforward movement of the mobile object or that the forward movementswitch is turned on during reverse movement of the mobile object. 11.The assist control device according to claim 3, wherein the control partis further configured to execute third brake processing to stop themobile object when determining that the operating switch is switchedbetween the first on state and the second on state during traveling ofthe mobile object.
 12. The assist control device according to claim 7,wherein the control part is further configured to execute the firstbrake processing with a brake force depending on the assist force of theelectric motor.
 13. The assist control device according to claim 1,wherein the control part is further configured to calculate the assistforce based on mobile object information regarding the mobile object.14. The assist control device according to claim 13, wherein the controlpart is configured to stop calculation of the assist force and set theassist force to a preliminarily set value until the mobile objectreaches a preliminarily set vehicle velocity from starting of assistcontrol.
 15. The assist control device according to claim 13, whereinthe control part is configured to stop calculation of the assist forceand set the assist force to a preliminarily set value until apreliminarily set time elapses from starting of assist control.
 16. Theassist control device according to claim 14, wherein the control part isconfigured to set the assist force to zero when the mobile object standsstill after elapse of a preliminarily set time.